1. Field of the Invention
The present invention relates to platform gate doors disposed on a platform at locations where passengers get on and off a train, and a control apparatus for the platform gate door device having photoelectric obstacle detectors disposed on door openings.
2. Description of the Related Art
Platform gate door devices are installed on the platforms of railways, monorail systems and new transportation systems at locations where passengers get on and off a vehicle, that is, at locations on the side edge of the platform corresponding to where the doors on the vehicle are positioned, in order to ensure safety of passengers and the like on the platform. According to the platform gate door device, the doors on the platform are opened and closed in response to the stopping of the vehicle and the opening and closing operation of the doors on the vehicle. When the vehicle is not stopped, in other words, when the vehicle is not in the track of the station or when the vehicle is traveling, the platform gate door is closed. In order to ensure safety, a photoelectric obstacle detector is disposed to detect whether an obstacle or a person is present between the platform gate door and the vehicle when the platform gate door is being closed or when the door is closed.
According to this type of photoelectric obstacle detector on the platform gate door device, a light emitter and a light receiver are disposed to face each other on either side of an opening, so that when an obstacle is present in the opening, the light output from the light emitter is not received by the light receiver, by which the detector detects the presence of an obstacle. However, when ambient light (disturbance light) such as sunlight enters the light receiver, it may be possible that the detector cannot detect the presence of an obstacle.
In order to overcome this problem, the platform gate door device according to the prior art suggested the following: adopting a hood member to be disposed over the light receiver of the photoelectric obstacle detector for shielding disturbance light; setting the optical axis connecting the light emitter and the light receiver aslant so that the incoming direction of disturbance light is out of range of directivity of the light receiver; preparing two sets of photoelectric obstacle detectors composed of the light emitter and light receiver, wherein the position of one set of light emitter and light receiver and the position of the other set of light emitter and light receiver are inversed so that the detector determines that an obstacle is present when both sets detect the presence of an obstacle; and modulating the output of the light emitter and attaching a filter to the receiver (refer for example to Japanese Patent Application Laid-Open Publication No. 2002-255026).
According to this prior art example, only the amount of disturbance light such as sunlight is restricted or the incident angle of the disturbance light is limited, and it does not completely prevent the entry of disturbance light taking certain incident angles. Furthermore, when two sets of obstacle detectors having the light emitter and the light receiver in inversed positions are disposed on each side of the door to detect the presence of an obstacle, if the results of detection of the two sets differ, it is difficult to determine which obstacle detector showed the true detection result. Moreover, there was a drawback according to the prior art method using the filter in that when strong sunlight was incident on the light receiver, the modulated infrared radiation could not be detected by the receiver, according to which the detector may erroneously determine that an obstacle is present.